Re: [PATCH v3 5/9] mm: remove CONFIG_DISCONTIGMEM

Stephen Brennan
2021-06-11T21:09:28Z

Mike Rapoport <rppt@kernel.org> writes:
> From: Mike Rapoport <rppt@linux.ibm.com>
>
> There are no architectures that support DISCONTIGMEM left.
>
> Remove the configuration option and the dead code it was guarding in the
> generic memory management code.
>
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
> include/asm-generic/memory_model.h | 37 ++++--------------------------
> include/linux/mmzone.h | 8 ++++---
> mm/Kconfig | 25 +++-----------------
> mm/page_alloc.c | 13 -----------
> 4 files changed, 12 insertions(+), 71 deletions(-)
>
> diff --git a/include/asm-generic/memory_model.h b/include/asm-generic/memory_model.h
> index 7637fb46ba4f..a2c8ed60233a 100644
> --- a/include/asm-generic/memory_model.h
> +++ b/include/asm-generic/memory_model.h
> @@ -6,47 +6,18 @@
>
> #ifndef __ASSEMBLY__
>
> +/*
> + * supports 3 memory models.
> + */

This comment could either be updated to reflect 2 memory models, or
removed entirely.

Thanks,
Stephen

> #if defined(CONFIG_FLATMEM)
>
> #ifndef ARCH_PFN_OFFSET
> #define ARCH_PFN_OFFSET (0UL)
> #endif
>
> -#elif defined(CONFIG_DISCONTIGMEM)
> -
> -#ifndef arch_pfn_to_nid
> -#define arch_pfn_to_nid(pfn) pfn_to_nid(pfn)
> -#endif
> -
> -#ifndef arch_local_page_offset
> -#define arch_local_page_offset(pfn, nid) \
> - ((pfn) - NODE_DATA(nid)->node_start_pfn)
> -#endif
> -
> -#endif /* CONFIG_DISCONTIGMEM */
> -
> -/*
> - * supports 3 memory models.
> - */
> -#if defined(CONFIG_FLATMEM)
> -
> #define __pfn_to_page(pfn) (mem_map + ((pfn) - ARCH_PFN_OFFSET))
> #define __page_to_pfn(page) ((unsigned long)((page) - mem_map) + \
> ARCH_PFN_OFFSET)
> -#elif defined(CONFIG_DISCONTIGMEM)
> -
> -#define __pfn_to_page(pfn) \
> -({ unsigned long __pfn = (pfn); \
> - unsigned long __nid = arch_pfn_to_nid(__pfn); \
> - NODE_DATA(__nid)->node_mem_map + arch_local_page_offset(__pfn, __nid);\
> -})
> -
> -#define __page_to_pfn(pg) \
> -({ const struct page *__pg = (pg); \
> - struct pglist_data *__pgdat = NODE_DATA(page_to_nid(__pg)); \
> - (unsigned long)(__pg - __pgdat->node_mem_map) + \
> - __pgdat->node_start_pfn; \
> -})
>
> #elif defined(CONFIG_SPARSEMEM_VMEMMAP)
>
> @@ -70,7 +41,7 @@
> struct mem_section *__sec = __pfn_to_section(__pfn); \
> __section_mem_map_addr(__sec) + __pfn; \
> })
> -#endif /* CONFIG_FLATMEM/DISCONTIGMEM/SPARSEMEM */
> +#endif /* CONFIG_FLATMEM/SPARSEMEM */
>
> /*
> * Convert a physical address to a Page Frame Number and back
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 0d53eba1c383..700032e99419 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -738,10 +738,12 @@ struct zonelist {
> struct zoneref _zonerefs[MAX_ZONES_PER_ZONELIST + 1];
> };
>
> -#ifndef CONFIG_DISCONTIGMEM
> -/* The array of struct pages - for discontigmem use pgdat->lmem_map */
> +/*
> + * The array of struct pages for flatmem.
> + * It must be declared for SPARSEMEM as well because there are configurations
> + * that rely on that.
> + */
> extern struct page *mem_map;
> -#endif
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> struct deferred_split {
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 02d44e3420f5..218b96ccc84a 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -19,7 +19,7 @@ choice
>
> config FLATMEM_MANUAL
> bool "Flat Memory"
> - depends on !(ARCH_DISCONTIGMEM_ENABLE || ARCH_SPARSEMEM_ENABLE) || ARCH_FLATMEM_ENABLE
> + depends on !ARCH_SPARSEMEM_ENABLE || ARCH_FLATMEM_ENABLE
> help
> This option is best suited for non-NUMA systems with
> flat address space. The FLATMEM is the most efficient
> @@ -32,21 +32,6 @@ config FLATMEM_MANUAL
>
> If unsure, choose this option (Flat Memory) over any other.
>
> -config DISCONTIGMEM_MANUAL
> - bool "Discontiguous Memory"
> - depends on ARCH_DISCONTIGMEM_ENABLE
> - help
> - This option provides enhanced support for discontiguous
> - memory systems, over FLATMEM. These systems have holes
> - in their physical address spaces, and this option provides
> - more efficient handling of these holes.
> -
> - Although "Discontiguous Memory" is still used by several
> - architectures, it is considered deprecated in favor of
> - "Sparse Memory".
> -
> - If unsure, choose "Sparse Memory" over this option.
> -
> config SPARSEMEM_MANUAL
> bool "Sparse Memory"
> depends on ARCH_SPARSEMEM_ENABLE
> @@ -62,17 +47,13 @@ config SPARSEMEM_MANUAL
>
> endchoice
>
> -config DISCONTIGMEM
> - def_bool y
> - depends on (!SELECT_MEMORY_MODEL && ARCH_DISCONTIGMEM_ENABLE) || DISCONTIGMEM_MANUAL
> -
> config SPARSEMEM
> def_bool y
> depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL
>
> config FLATMEM
> def_bool y
> - depends on (!DISCONTIGMEM && !SPARSEMEM) || FLATMEM_MANUAL
> + depends on !SPARSEMEM || FLATMEM_MANUAL
>
> config FLAT_NODE_MEM_MAP
> def_bool y
> @@ -85,7 +66,7 @@ config FLAT_NODE_MEM_MAP
> #
> config NEED_MULTIPLE_NODES
> def_bool y
> - depends on DISCONTIGMEM || NUMA
> + depends on NUMA
>
> #
> # SPARSEMEM_EXTREME (which is the default) does some bootmem
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index aaa1655cf682..6fc22482eaa8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -331,20 +331,7 @@ compound_page_dtor * const compound_page_dtors[NR_COMPOUND_DTORS] = {
>
> int min_free_kbytes = 1024;
> int user_min_free_kbytes = -1;
> -#ifdef CONFIG_DISCONTIGMEM
> -/*
> - * DiscontigMem defines memory ranges as separate pg_data_t even if the ranges
> - * are not on separate NUMA nodes. Functionally this works but with
> - * watermark_boost_factor, it can reclaim prematurely as the ranges can be
> - * quite small. By default, do not boost watermarks on discontigmem as in
> - * many cases very high-order allocations like THP are likely to be
> - * unsupported and the premature reclaim offsets the advantage of long-term
> - * fragmentation avoidance.
> - */
> -int watermark_boost_factor __read_mostly;
> -#else
> int watermark_boost_factor __read_mostly = 15000;
> -#endif
> int watermark_scale_factor = 10;
>
> static unsigned long nr_kernel_pages __initdata;
> --
> 2.28.0